The International Pop Underground convention was a utopian dream come to life, and could have only happened in Olympia, the capital of Washington state in the Pacific north-west of the US. An hour outside Seattle, Olympia is a college town with a hippie hangover and approximately nothing fun to do – the underground rock scene in 1991 consisted of the same few dozen individuals seeing each other's bands in basements. The Olympian conception of rock'n'roll was singular and thoughtfully naive: sweetness, inclusion and amateurism were held in high regard; the typical rock hallmarks of macho preening, guitar solos and professionalism were somewhere between verboten and unfashionable.

Olympia was (and still is) home to the K Records label – helmed, in part, by Calvin Johnson of the groups Beat Happening and Dub Narcotic Sound System. In 1991, Johnson, along with his K colleague Candice Pedersen and a coterie of locals, organised the six-day International Pop Underground convention. Johnson saw the IPU as a way to gather all the like-minded weirdos and underground bands from across the country in one place so they could hang out. The convention mixed rock shows with non-rock fun – including a cakewalk, picnics, poetry readings and a screening of Planet of the Apes.

The convention's first night would be an auspicious one, one that nearly 20 years later still overshadows the rest of IPU. Billed as Love Rock Revolution Girl Style Now, what became known as Girl Night assembled some 15-odd all-female bands on one bill at the Capitol theatre. Teenage upstarts were mixed with feminist acts like Bratmobile and Suture, and local progenitors including Jean Smith and Lois Maffeo.

It would be the first show for a teenage Corin Tucker, performing in her pre-Sleater-Kinney duo, Heavens to Betsy. Their three-song set of intensely personal songs, including one about avenging sexual abuse, would be breathlessly recounted in all the major grrrl-zines. Girl Night was also the debut performance for Rose Melberg, who was on the cusp of forming the influential all-female pop group Tiger Trap. It saw one of the first performances by the Spinanes, and the debut solo performance from Tobi Vail (Bikini Kill, the Go Team) and Christina Billotte (Autoclave, Slant 6).

That night, the stage of the Capitol theatre was graced by more than a dozen women who would become leading lights in the American punk underground, and whose work would define punk feminism for the decade that followed. While Girl Night was not the start of this "Riot Grrrl" movement – there had already been zines, meetings and conspiratorial plans hatched – it was the movement's galvanising spark. It was time to be heard.

While there wasn't a particular need to set aside a night for just the women – the convention's bills were rife with women, and the scene had a strong matriarchal streak – the female organisers had pushed for one and made a special circumstance that included unknowns, decrying the idea that you had to truly know what you were doing before you started a band. The bands on Girl Night inspired one another and helped coalesce the importance of support and networking, putting the pieces in place for Riot Grrrl's musical manifestos to come.

The attendees at the International Pop Underground convention had no idea that they were in the twilight of an era – approximately one month later some former locals called Nirvana would ignite the world with Smells Like Teen Spirit. The underground would divide into two halves: one made up of bands wishing to be the next Nirvana, vying for major label contracts, the other of fiercely indie forces who would just dig in deeper, bracing themselves against commercial interests. While many bands and labels in the nearby city of Seattle would succumb to commerce's lure, the ideals of the IPU – the anti-professional stance, exaltation of amateurs, resistance to hierarchy, radical feminism – stood in stark relief against the grunge gold rush.

As Nirvana exploded, the gospel according to Riot Grrrl began to spread through word of mouth, fanzines and tapes traded between penpals. Word of the radical girl power underground would expand rapidly with every Bikini Kill record release – and its UK counterpart was found in the London group Huggy Bear.

Girl Night had unleashed something new and powerful; it had shown the girls a glimpse of a dazzling future of feminist truth and amps dialled to 10 – and there would be no going back.